1. Field of the Invention
The present invention relates to a traffic sign detecting method and a traffic sign detecting device.
2. Description of the Related Art
As development is continuing on an intelligent transportation system (ITS), and the intelligent transportation system has been widely used, a research on a traffic sign detecting technology has gradually garnered attention. Since standards of traffic signs adopted by various countries in the world are basically the same, a traffic sign detecting technology developed with regard to traffic signs of one country may be applied in other countries without any modifications or only with slight adjustments. As a result, this kind of traffic sign detecting technology has universal applicability.
Up to now, a certain amount of development has been carried out in the field of traffic sign detection; for example, many patents or patent applications have been made. In conventional techniques, color, shape information, or geometric features of traffic signs are utilized for performing detection and recognition with regard to the traffic signs in general. After the traffic signs are recognized, a driver may be notified of the recognized traffic signs in a manner of audio or visual information.
In the following cited Reference No. 1, a traffic sign detecting method is proposed. According to this method, pairs of colors and shapes are proposed by analyzing the basic color and the geometric shape of traffic signs. On the basis of this, relationship models of the traffic sign color and the traffic sign geometric shape are created. For example, a pair of (red, triangle) corresponds to a “prohibitive sign group”. By employing the relationship models, it is possible to conduct detection with regard to the traffic signs. In this reference, seven such pairs of colors and shapes are created. However, in this method, information of color and shape is only used for performing the detection with regard to the traffic signs. Furthermore the shape information used in this method only corresponds to the outer shape of the traffic signs; in other words, this method does not relate to the application of the inner shape information of the traffic signs. As a result, this method may only be utilized for recognizing to what group a traffic sign usually belongs, or to put it another way, this method may not carry out accurate detection with regard to the traffic sign. In addition, sometimes it is impossible to totally distinguish the traffic sign from other objects only by using the color and the outer shape information.
In the following cited Reference No. 2, a method for traffic sign recognition is proposed. This method employs rotation and scale-invariance to perform pattern matching, and then recognizes a candidate traffic sign by adopting a way of calculating a degree of confidence. In this method, due to complexity of a scene, the pattern matching may generate a large amount of candidate traffic signs, i.e., traffic signs waiting for recognition, in some cases. If the number of the traffic signs waiting for recognition is too big, then the processing speed of this method may be badly affected. This results in lack of “real time” usually required by a traffic sign recognizing system.
In the following cited Reference No. 3, a method of detecting and recognizing traffic signs is proposed. In this method, an image is divided into two parts. As for one of the two parts, its color and shape information is utilized to carry out detection and recognition with regard to the traffic signs, and as for another one, it is utilized for achieving other assistant driving functions. However, in this method, only the color and the shape information is considered, and this method is only adapted for detecting a circular (a rectangle in the United States) “speed-limit” sign.
In a traffic sign system, it is possible to render the color and the shape of a traffic sign obviously different from that of other objects by carrying out design, but actually, in some scenes, particularly in a case where only the outer outline information of a traffic sign is utilized, it may be impossible to perfectly distinguish the traffic sign from the surrounding objects. On the other hand, since there are nearly one hundred different traffic signs in a traffic sign system of a country in general, a common object recognizing method based on color and shape may dramatically cost time when concretely recognizing a specific traffic sign; as a result, this kind of method is difficult to satisfy the requirement of processing time in actual use. In addition, after the traffic sign is recognized, when it is notified to a driver as a prompt or warning message, most of the conventional techniques do not take into account the concrete meaning of the traffic sign or its warning level.    Cited Reference No. 1: Chinese Patent Application Publication No. 101702197 A    Cited Reference No. 2: US Patent Application Publication No. 2009/0074249 A1    Cited Reference No. 3: US Patent Application Publication No. 2008/0137908 A1